Recently there has become known a radio antenna of this type that is referred to as an "on glass or glass-mount" antenna. Such antennas comprise a radiating element that is mounted externally on a glass window or windscreen of the vehicle and an internal connector that is coupled to radio apparatus within the vehicle and is coupled to the external antenna by a capacitor plate mounted to the internal surface of the windscreen and cooperating with an external capacitor plate electrically coupled to the external antenna. The overlapping internal and external capacitor plates together with the dielectric material of the glass form a capacitor that couples the internal connector to the external antenna and may form part of a matching circuit that also serves to match the impedance of the antenna to the radio apparatus. An example of an internal connector utilising this arrangement is described in European Patent No. 0456350.
The external antenna in such an arrangement is, apart from the coupling capacitor, of conventional form and comprises the normal rod or whip-like conductor that has a length corresponding to a fraction of the working wavelength and is loaded by an inductance that is usually incorporated in the whip to provide base or centre loading of the antenna.
Whilst an external antenna of this kind is functionally effective, in the context of a motor vehicle it has the severe disadvantage that it is vulnerable to vandalism when the vehicle is unattended.